As shown in FIG. 1, a prior art zipper head 10 has a head 12, a pull tab 13 fastened with the head 12, and a pulling member 14 fastened with the pull tab 13 to facilitate the pulling of the pull tab 13. Located between pull tab 13 and the pulling member 14 is a retaining ring 15 which is engaged with a hook 16 of the pull tab 13. Such a prior art zipper head 10 as described above is defective in design in that the hook 16 must be made by molding, and that the hook 16 is not cost-effective, and further that the rejection rate of the hook 16 is relatively high.
As shown in FIGS. 2 and 3, another prior art zipper head 20 has a pull tab 23 with a hooked portion 24. Located between the hooked portion 24 and a beam 25 of the pull tab 23 is an insertion slot 26 in which a body 271 of a U-shaped elastic piece 27 is lodged such that the curved portion 273 is connected with the beam 25, and that an opening of the hooked portion 24 is sealed off by the body 272. This prior art zipper head 20 is defective in design in that the elastic piece 27 is poorly located, and that the elastic piece 27 is thus prone to become disengaged with the insertion slot 26. The improved version of the zipper head 20 is provided with two protruded portions 28, which are fastened with the curved portion 273 of the elastic piece 27 by rivets. Such an improved version of the zipper head 20 is not cost-effective, and that the protruded portions 28 are too small to fasten securely with the elastic piece 27.
As shown in FIGS. 4 and 5, the prior art zipper head 30 has an elastic piece 35. The elastic piece 35 has a body 351, which is provided with an elastic urging portion 36. As the elastic piece 35 is inserted into the beam 33 and the insertion slot 34 of the pull tab 31, the urging portion 36 urges the beam 33 so as to bring about the locating effect. The elastic piece is capable of bringing about a better locating effect and can be easily assembled. However, the zipper head of the present invention is defective in design in that the front end of the ring portion 38 of the pull member 37 is extended into a place located between the two piece bodies 351 and 352 at the time when the pull member 37 is in use, and that the front end of the ring portion 38 puts a pressure on the urging portion 36, thereby causing the free end of the urging portion 36 to be pushed. The urging portion 36 is no longer urging the beam 33. As a result, the elastic piece 35 is prone to become disengaged with the pull tab 31.